One of the first projects I did a couple years ago, was designing a custom freezer monitoring system. It's end purpose was monitoring -80°C freezer, but they where actually tested down to -196°C in liquid nitrogen.

The system communicates wirelessly with two gateways, by using a Zigbee mesh network between multiple nodes. Both gateways are operating 24/7, but the system does run perfectly fine on one gateway. The second gateway is purely redundant to reduce potential downtime.